A kind of magnetic resonance imaging system based on totally digitilized spectrometer
Technical field
The present invention relates to a kind of medical equipment, be specifically related to a kind of magnetic resonance imaging system based on totally digitilized spectrometer.
Background technology
Magnetic resonance imaging spectrometer is the nucleus equipment in the magnetic resonance imaging system.Its structure has directly determined magnetic resonance imaging system complexity and image quality.What domestic application was more is the MR6000 spectrometer (http://www.mrsolutions.co.uk/) of Britain MR SOLUTIONS company, below it is briefly described.
1. spectrometer receiving system
This spectrometer places in the equipment room, it receives sampling system and is positioned at spectrometer, generally, increase along with receive path, also can correspondingly increase from the coaxial cable quantity of drawing between magnet, because the NMR signal voltage that receives is the maximum of the voltage of free damping signal (FID), provided by formula 1, as seen itself and magnetic field intensity are proportional by force.
So for low (field intensity is less than 0.5 tesla), the signal that receives can be very faint, about the order of magnitude of microvolt.After coil-induced FID signal demand one-level low noise amplification and two stage gains amplification, could deliver to MR6000 spectrometer receiving terminal by coaxial cable.In order to satisfy the requirement of system imaging signal to noise ratio, the low-noise amplifier of one-level must satisfy the characteristic of low-noise factor, is generally less than 1dB, and its gain generally can be very not big like this, about about 28dB.In order to allow the analog-digital converter of spectrometer end can bring into play its characteristic, two stage gains are amplified to few about 30dB.In low field system, increasing receive path not only needs to increase coaxial cable quantity, also needs to increase the secondary pre-amplifier unit of same quantity so.When system cost increased so, a large amount of connection cords and amplifying unit also can strengthen the reception interference between signals, caused the imaging signal to noise ratio of imaging system to descend.
For High-Field (field intensity is greater than 0.5 tesla), though the NMR signal that receives is bigger than low field system intensity, but owing to the increase along with home court intensity, by Larmor formula (2), the frequency that receives the NMR signal can increase, for example 3T field intensity system, the signal center frequency that receives is 127.728MHz, generally, coaxial cable is far longer than low frequency signal to the decay of high-frequency signal, and the discontinuous meeting of the seam impedance of coaxial cable increases the weight of this decay in addition.So when increasing receive path, the increase of number of cables, what bring is the high frequency attenuation that receives the NMR signal, the imaging signal to noise ratio of imaging system descends.
B
0: static magnetic field strength, γ: gyromagnetic ratio, f: receive the NMR signal frequency
So still be high field system in low field system no matter, the conventional magnetic resonance imaging spectrometer, the as above MR6000 in the example, along with the increase of receive path, image quality descended when system cost increased.
2. spectrometer radio frequency transmitting system
The conventional magnetic resonance spectrometer system as, the MR6000 spectrometer, radio frequency sends the same with its receiving system, is to be connected to radio-frequency power amplifier by spectrometer by coaxial cable also, also needs in addition the radio frequency output switching signal is linked on the radio-frequency power amplifier by coaxial cable.This control mode spectrometer and radio-frequency (RF) power amplification does not first have complete electrical isolation, second spectrometer is in passive position, it also is the actual working state that spectrometer can not be read power amplifier, this calibration and maintenance for system brings very big complexity, can not realize the remote maintenance to whole magnetic resonance imaging system, increase maintenance cost.
3. the gradient transmitting system of spectrometer
The conventional magnetic resonance spectrometer system as, the MR6000 spectrometer, gradient waveform output exports gradient amplifier to by the D connector difference, the problem of the electric incomplete isolation of the same spectrometer that exists and gradient amplifier, in addition, the degree of accuracy of the gradient waveform of sending from spectrometer directly affects the output current of gradient amplifier, but owing to is subjected to the degree of accuracy of the gradient waveform that connecting line, device effects of distribution parameters gradient amplifier obtain and is difficult to export consistent with spectrometer.Accurate adjustment to gradient amplifier electric current output stage is difficult to use some digital algorithms in addition, and this design that gradient is amplified brings certain degree of difficulty.
4. doctor's operating board
The conventional magnetic resonance spectrometer system as, the MR6000 spectrometer separates with doctor's operating board, doctor operation is undertaken by Ethernet or other modes special-purpose computer of action need and the spectrometer of magnetic resonance imaging system.The operation easier that has not only increased doctor's pair spectrometer so also makes systematic jitters increase, the also corresponding increase of cost of same system.
In order to overcome above-mentioned a series of shortcomings and deficiency based on tradition spectrum magnetic resonance imaging system, need a kind of magnetic resonance imaging system based on totally digitilized spectrometer to improve image quality and reduction system cost and maintenance cost.
Summary of the invention
At above-mentioned weak point, the objective of the invention is to propose a kind of magnetic resonance imaging system based on totally digitilized spectrometer, improve image quality, reduce system cost and maintenance cost.
The technical scheme that the present invention adopts for achieving the above object is: a kind of magnetic resonance imaging system based on totally digitilized spectrometer, the total digitalization spectrometer is integrated special-purpose computer and the digitized NMR signal receiving unit that is connected with this special-purpose computer, digitized radio-frequency (RF) excited transmitting element, digitized gradient waveform transmitting element and the management of digitized magnet and patient monitoring unit;
Described digitized NMR signal receiving unit has N receive path, and each receive path connects a receiving front-end module in the receiving front-end unit, sends digital controlled signal to the receiving front-end unit; Described receiving front-end module has M and receives AFE (analog front end) passage and the data processing unit that the signal that receives the AFE (analog front end) channel transfer is handled.
Described digitized radio-frequency (RF) excited transmitting element is connected with the digital RF power amplifier, digitized radio-frequency (RF) excited waveform is sent to the digital RF power amplifier, and the control interface by the digital RF power amplifier, the output after control and read-back power are amplified and the duty of digital RF power amplifier;
Described digitized gradient waveform transmitting element is connected with the digital gradient amplifier, and the digitized gradient waveform is sent to the digital gradient amplifier, controls and output current, transmitting power and the duty of the digital gradient amplifier that reads back;
The management of described digitized magnet and patient monitoring unit manage with magnet and the patient monitoring front end is connected, and read the work state information of magnet system and to patient's monitor message.
The integrated doctor's console function of described special-purpose computer, the operation doctor can carry by means of the display device that is connected in totally digitilized spectrometer and mouse, keyboard to system closely or operated from a distance.
Described special-purpose computer operation magnetic resonance imaging system software.
Described digitized NMR signal receiving unit all is connected by high-speed figure optical fiber, cable or wireless mode with magnet management and patient monitoring front end with digital gradient amplifier, the management of described digitized magnet and patient monitoring unit with digital RF power amplifier, described digitized gradient waveform transmitting element with receiving front-end unit, described digitized radio-frequency (RF) excited transmitting element.
Described receiving front-end module is NMR signal process impedance matching, noiselike signal conditioning, variable gain and bandwidth filtering from the coil coupling, be untreated digital NMR signal through analog digital conversion again, the untreated digital NMR signal in M road gathers to a data processing unit and carries out Digital Signal Processing.
Described noiselike signal conditioning comprises amplitude limit, amplification and the Filtering Processing to signal.
Described data processing unit comprises and comprises the Digital Down Convert unit successively, variable bandwidth filter and channel data encoder.
Described receiving front-end module is built in coil inside, perhaps is connected to the coil outside by coaxial cable.
Described digitized radio-frequency (RF) excited transmitting element is by the control data of EBI reception from special-purpose computer, the waveform table radio frequency waveform that obtains launching of tabling look-up is transformed to the digital band signal through Digital Up Convert, becomes optical signal by opto-electronic conversion again and be sent to the digital RF power amplifier through optical fiber.
Described digitized gradient waveform transmitting element is by the gradient control information of EBI reception from special-purpose computer, under the control of gradient transmitting element controller, corresponding X-axis controller, Y-axis controller, Z axis controller, obtain gradient control information on X, Y, the Z direction, unified after the gradient waveform coding, become optical signal by photoelectric conversion unit and reach the digital gradient amplifier through optical fiber.
The present invention has the following advantages:
1. reduced the receive path wiring quantity.4 receive path magnetic resonance imaging systems are reduced to 1 optical fiber receive path by 4 coaxial receive paths; 16 receive path magnetic resonance imaging systems are reduced to 1 optical fiber receive path by 16 coaxial receive paths; 128 receive path magnetic resonance imaging systems are reduced to 4 optical fiber receive paths by 128 coaxial receive paths;
2. improved reception NMR signal transfer quality, the simulation of NMR conversion of signals has improved the system imaging signal to noise ratio for the digital NMR signal of handling transmits;
3. exact figure control is carried out in the radio frequency power amplification;
4. gradient amplifier is carried out exact figure control;
5. system cost and maintenance cost have been reduced.
Description of drawings
Fig. 1 is the magnetic resonance imaging system formation block diagram based on totally digitilized spectrometer;
Fig. 2 constitutes block diagram for receiving front-end module;
Fig. 3 constitutes block diagram for connecing the AFE (analog front end) passage;
Fig. 4 is that single channel digital NMR signal receiving unit constitutes block diagram;
Fig. 5 is that digitized radio-frequency (RF) excited transmitting element constitutes block diagram;
Fig. 6 is that digitized gradient waveform transmitting element constitutes block diagram;
Fig. 7 is the magnetic resonance imaging system formation method flow chart of steps based on totally digitilized spectrometer;
Fig. 8 is that 4 passage receiving front-end unit constitute block diagram;
Fig. 9 is that 16 passage receiving front-end unit constitute block diagram;
Figure 10 is that 128 passage receiving front-end unit constitute block diagram;
Figure 11 is that 4 passage digitized NMR signal receiving units constitute block diagram.
The specific embodiment
The present invention is described in further detail below in conjunction with drawings and Examples.
As shown in Figure 1, totally digitilized spectrometer is integrated digitized NMR signal receiving unit; Digitized radio-frequency (RF) excited transmitting element; Digitized gradient waveform transmitting element; The management of digitized magnet and patient monitoring unit; Special-purpose computer.
Shown in Fig. 2,3,4, digitized NMR signal receiving unit has N (N is integer) individual high-speed figure receive path and a receiving front-end control channel.Each high-speed figure receive path by high-speed figure optical fiber, includes but not limited to high-speed figure optical fiber, is connected to a receiving front-end module in the receiving front-end unit.The receiving element control channel of digitized NMR signal receiving unit is connected to the control interface of receiving front-end unit by high-speed figure optical fiber.Wherein the receiving front-end unit can be divided into reception AFE (analog front end) passage, receives digital front-end two parts.Receiving the AFE (analog front end) passage is made up of impedance matching network, noiselike signal conditioning unit, variable gain and bandwidth filter unit, high speed analog-to-digital conversion unit.Receiving the AFE (analog front end) passage can be an independently integrated circuit, also can be combined by discrete device, and it is responsible for direct-coupled receiving coil induction NMR signal is become the digital signal of quantification.Data processing unit is made up of Digital Down Convert, bandwidth varying digital filter, channel data coding.Data processing unit is realized with the FPGA device, can certainly realize with other integrated circuit, its NMR signal of being responsible for having quantized carries out Digital Signal Processing, NMR signal after the processing is through the high speed optoelectronic modular converter, be converted to optical signal, by high-speed figure optical fiber, reach the digitized NMR signal receiving unit of spectrometer.
As shown in Figure 5, digitized radio-frequency (RF) excited transmitting element, by the radio-frequency (RF) excited transmitting element control data of EBI reception from special-purpose computer, the waveform table radio frequency waveform that obtains launching of tabling look-up is transformed to the digital band signal through Digital Up Convert, becomes optical signal by opto-electronic conversion then and be sent to the digital RF power amplifier through optical fiber.Radio frequency transmitting element controller receives from the status information of digital RF power amplifier and uses for imaging system.
As shown in Figure 6, digitized gradient waveform transmitting element, by the gradient control information of EBI reception from special-purpose computer, under the control of gradient transmitting element controller, corresponding X-axis controller, Y-axis controller, Z axis controller, obtain gradient control information on X, Y, the Z direction, unified after the gradient waveform coding, become optical signal by photoelectric conversion unit and reach the digital gradient amplifier through optical fiber.Simultaneously some status informations such as the output current of digital gradient amplifier, power are sent to the control interface of digitized gradient waveform transmitting element with the optical signal form with optical fiber, use for imaging system.
Wherein, the management of digitized magnet and patient monitoring unit by magnet management and patient monitoring front end, with the duty of magnet system, are sent to spectrometer as temperature or other relevant informations by digital fiber.Simultaneously, also monitor messages such as patient's electrocardio, breathing can be sent to spectrometer by digital interface.
Wherein, special-purpose computer is moving magnetic resonance imaging system software, and totally digitilized magnetic resonance imaging spectrometer is being controlled each unit or parts in the imaging system by it, as receiving front-end unit, digital gradient amplifier, magnet management and patient monitoring front end.In addition, special-purpose computer is also integrated, and the doctor grasps uses the platform function
The invention also discloses a kind of magnetic resonance imaging system based on totally digitilized spectrometer, this imaging system is integrated digital NMRization receiving element, digitized radio frequency transmitting element, digitized gradient transmitting element, digital magnet managerial function and digital patient monitoring unit.Digitized NMR receiving element wherein, support the individual NMR signal receive path of N (N is integer), when system increases new receive path, system only needs to increase corresponding analog front-end module, the cable number of system interconnect does not increase, cost is not multiplied, and has alleviated system upgrade and maintenance cost yet; Wherein, digitized radio frequency transmitting element is sent to the digital RF power amplifier with the digital RF waveform, can accurately control the output of radio-frequency power amplifier simultaneously; Wherein, digitized gradient transmitting element, the digital gradient waveform is sent to the digital gradient amplifier, can accurately control simultaneously the output current of gradient amplifier, for the gradient amplifier design, can use some higher digital algorithms of precision, to improve gradient amplifier response time and output current accuracy; Wherein digital magnet administrative unit can be sent to spectrometer in real time with the status information of magnet, is convenient to spectrometer to the real-time control of magnet, operates as shimming; Wherein, digital patient monitoring unit can be sent to spectrometer with the form of digital signal by optical fiber with information such as patient's electrocardio, breathing, positions, in real time so that the application of some senior scanning sequences needs;
As shown in Figure 7, nuclear magnetic resonance of the present invention is controlled radio-frequency power amplifier with digital form, with digital form control gradient amplifier; NMR receives signal with the digital form transmission; Method step when meanwhile, spectrometer is carried out scanning sequence:
Step 1, the scanning beginning;
Step 2, pre-scan phase, imaging system is to receiving front end unit, digital RF power amplifier, digital gradient amplifier calibration, and duty detects, and normally then carry out step 2, otherwise fault processing;
Step 3, sweep phase sends digital RF, digit gradient signal, receives digital NMR signal;
Step 4, in the imaging reconstruction stage, imaging software carries out image reconstruction to digital NMR signal, under the multisequencing queuing situation, carry out step 1;
Step 5, scanning is finished, and prepares next sequence of scanning.
This method is controlled radio-frequency power amplifier, gradient amplifier in digital mode, has improved control accuracy and motility; Transmit NMR in digital mode and receive signal, improve signal transfer quality, and then improved the signal to noise ratio of imaging; During multisequencing formation scanning, carry out step 2 simultaneously in the imaging reconstruction stage of step 4, to reduce sweep time, accelerate image taking speed.
The present invention is based on magnetic resonance imaging system and the method for totally digitilized spectrometer, embodiment can be followed according to market demand flexible configuration receive path number.Below only list the embodiment that 3 kinds of typical cases use always, be respectively 4 receive path magnetic resonance imaging systems, 16 receive path magnetic resonance imaging systems and 128 receive path magnetic resonance imaging systems.Certainly, below listed embodiment do not represent whole embodiments that the present invention states, based on any embodiment of inventive concept, still within the specific embodiment of the present invention scope.
Embodiment (1): 1:4 receive path magnetic resonance imaging system, as Fig. 8,11.
Because it is more extensive that 4 receive path magnetic resonance imaging systems are used, the open mri system that has now installed is still based on 4 receive paths, so 4 receive paths total digitalization spectrometer still has positive effect to the existing capable upgrading of old magnetic resonance imaging system equipment.The receiving front-end unit of 4 receive paths total digitalization spectrometer receives 1~4,1 reception of AFE (analog front end) passage data processing unit, control unit, Clock management and opto-electronic conversion by 4 and forms.Each receives an AFE (analog front end) passage corresponding receiving coil (not indicating among the figure) respectively, receive the AFE (analog front end) channel function and constitute block diagram as shown in Figure 3, its effect will be Direct Digital NMR signal from the simulation of NMR conversion of signals of receiving coil coupling, deliver to photoelectric conversion module after Digital Down Convert, variable bandwidth filter, the channel data coded digital signal of 4 tunnel Direct Digital NMR signals through receiving data processing unit handled and become optical signal is delivered to spectrometer through optical fiber digitized NMR signal receiving unit.Digitized NMR signal receiving unit, to through opto-electronic conversion, channel data decoding, reception FIFO 4 road NMR reception signal be delivered to through system bus by EBI from the digital NMR signal of receiving front-end is special-purpose computer, and system imaging software is by this to checking the object imaging.
Embodiment (2): 2:16 receive path magnetic resonance imaging system, as Fig. 9.
Use for High-Field, 16 receive paths are the basic configuration mode of totally digitilized spectrometer.The receiving front-end unit of 16 receive paths total digitalization spectrometer receives 1~16,1 reception of AFE (analog front end) channel number data processing unit, control unit, Clock management and opto-electronic conversion by 8 and forms.Each receives respectively corresponding 2 receiving coils of AFE (analog front end) passage, receive the AFE (analog front end) channel function and constitute block diagram as shown in Figure 3, its effect will be Direct Digital NMR signal from the simulation of NMR conversion of signals of receiving coil coupling, deliver to photoelectric conversion module after Digital Down Convert, variable bandwidth filter, the channel data coded digital signal of 16 tunnel Direct Digital NMR signals through receiving data processing unit handled and become optical signal is delivered to spectrometer through optical fiber digitized NMR signal receiving unit.Digitized NMR signal receiving unit, to through opto-electronic conversion, channel data decoding, reception FIFO 16 road NMR reception signal be delivered to through system bus by EBI from the digital NMR signal of receiving front-end is special-purpose computer, and system imaging software is by this to checking the object imaging.
Embodiment (3): 3:128 receive path magnetic resonance imaging system, as Figure 10.
Use for High-Field, 128 receive paths are the advanced configuration mode of totally digitilized spectrometer.This configuration mode is fit to some senior scanning sequences and uses.128 receive paths total digitalizations spectrometer has 4 receiving front-end unit and corresponding 4 passage digitized NMR signal receiving units with it, and each receiving front-end unit receives 1~32,1 reception of AFE (analog front end) channel numbers data processing unit, control unit, Clock management and opto-electronic conversion by 8 and forms.Each receives respectively corresponding 4 receiving coils of AFE (analog front end) passage, receive the AFE (analog front end) channel function and constitute block diagram as shown in Figure 3, its effect will be Direct Digital NMR signal from the simulation of NMR conversion of signals of receiving coil coupling, deliver to photoelectric conversion module after Digital Down Convert, variable bandwidth filter, the channel data coded digital signal of 32 tunnel Direct Digital NMR signals through receiving data processing unit handled and become optical signal is delivered to spectrometer through optical fiber 4 passage digitized NMR signal receiving units.4 passage digitized NMR signal receiving units, to through 4 opto-electronic conversion, channel data decoding, reception FIFO 128 road NMR reception signal be delivered to through system bus by EBI from 4 way word NMR signals of receiving front-end is special-purpose computer, and system imaging software is by this to checking the object imaging.